Abstract: Sexually Transmitted Infections including HIV/AIDS are among the major sexual and reproductive health problems facing Tanzania. This study was carried in Chamwino District in Central Tanzania to determine prevalence of high-risk sexual behaviour and identify the correlates of high -risk sexual behaviour among youth. Data were collected from a random sample of 600 youth aged between 15 – 24 years using a structured questionnaire with closed-ended and open-ended questions. Data were analyzed using Statistical Package for Social Sciences (SPSS) version 18. The results indicate that 31.8% were engaged in high-risk sexual behaviour (e.g. having more than two partners in the past 12 months and not using condom). Chances for engaging in high-risk sexual behaviour by youth increased with lack of comprehensive knowledge on HIV/AIDS (OR = 1.94; 95% CI = 1.23 – 3.09), but decreased with having secondary education and above (OR = 0.77; 95% CI = 0.70 – 0.84). The Likelihood also increased with having close friends that are sexuallyactive (OR = 1.72; 95% CI = 1.32 – 2.26), if used alcohol (OR = 2.82; 95% CI = 1.53 – 5.27), and if engaged in transactional sex (OR = 4.68; 95% CI = 3.30 – 6.65). Overall, findings show that a substantial proportion of youth in the study population are engaged in high-risk sexual behaviour. It is recommended that more education on HIV/AIDS among youth should be emphasized in the study area.